Sterically congested tripodal phosphites: conformational analysis, solid-state polymorphism, metal complexation, and application to the asymmetric hydrosilation of ketones.

The synthesis as well as isolation and crystallographic analysis of two solid-state polymorphs of the tripodal ligand tri[2,2',2' '-tris[(2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]ethyl]amine (3) is described. Form I crystallized from ethyl acetate in the space group P2(1)/n with the unit-cell parameters a = 20.070(10) A, b = 17.

Atomic Proximity Due to Molecular Congestion: Rational Design of Bis(phosphite) Ligands by Restriction of Molecular Motion(1).

The synthesis and conformational analysis of the sterically congested bis(phosphite) ligand {2-{1-{3,5-(t)Bu(2)-2-[2,2'-CHCH(3)(4,6-(t)Bu(2)C(6)H(2)O)(2)PO]C(6)H(2)}Et}-4,6-(t)Bu(2)C(6)H(2)O}(PhO)(2)P (5) are reported. X-ray crystallographic, dynamic (31)P{(1)H} NMR, NOE, DNOE, CP-MAS (31)P NMR, and calculational studies of 5 as well as the structurally related bis(phosphites) 1 and 6 suggest that the conformational freedom of the molecule is severely restricted because of geometric restraints due to steric congestion. A through-space mechanism of coupling is suggested to explain the observed eight-bond P-P J coupling of 27.